Dating your martin guitar
rights to the Sigma brand name and trademark had been allowed to lapse by C. Louis Music of Missouri, AMI is not allowed to use the brand name "Sigma" in the U. The model and serial numbers were usually stamped on in ink, but some are known to have been hand-penned. These will have a 4, 5 or 8 digit (7*0XXXXX) serial number stamped or hand written on them. The 'Purple' label (c1972 onward): These are again white labels that had gold & black lettering but this time with a border, often pinkish-brown or violet in color. Pearl "SIGMA" block inlay between 19th and 20th fret. They have a paper label stating "Inspected and Guaranteed by Levin" and "Sigma Guitars" "est 1970" is inlaid on the headstock in abalone.
The Back Brace Brand: From 1978 through 1983; 1978 being a transition year, one might find the center back brace is pressure stamped, or "branded" in a football shape stating Sigma Guitars/Made in Japan/For/C. During later Korean made years (c1990,) Sigma transitioned back to paper labels and they stayed that way until the end of production in Indonesia in 2007. These models have saddles with each string individually compensated, yielding superb intonation.
distributor is now Six String Brokerage LLC, Nazareth, Pa.
Other physical indicators or attributes, such as finish, trim, tuners, etc., can help determine the approximate construction date of a particular example, but almost never exactly. It is not known at this time just how many D-10's were built but it is believed by some, and indicated by the number up for saleat any given time that production ran into the thousands, not limited to 100 as previously rumored. Martin memo dated August 7, 1980 further discusses 'economically uncorrectable' cosmetic flaws in the D-10 and how they were to be indicated by the inspectors: "The flawed instruments were graded into 2 categories depending on the nature of the blemishes and were stamped on the back center strip accordingly.
The issue of whether or not Sigma guitars are solid wood or "plywood"laminate wood has been a source of controversy and confusion for many years now.
All known Sigma guitars have laminated sides and back wood. This is understandable since the Martin customer service department now responds to individual inquiries stating "all" Sigma's had laminate back/sides, while Sigma catalogs from the early 70s list the back/side wood as "Matched." (edit: "Matched" does not mean solid, but is a careful marketing nomenclature for laminate to confuse potential buyers.) In the 70's Sigma produced a line of guitars with model numbers starting with 52S, e.g., 52SDM-5, 52SDR-7 and 52SGCS-7. Adjustable rosewood bridge to approximately 1975, non-adjustable thereafter.